[3.13] gh-130917: update timer and workload in test_signal (GH-130918) (#130969)

The workload to advance the virtual timeout is too lightweight for some
platforms. As result the test goes in timeout as it never reaches the
end of the timer. By having a heavier workload, the virtual timer
advances rapidly and the SIGVTALRM is sent before the timeout.
(cherry picked from commit 7879081)

Co-authored-by: Diego Russo <diego.russo@arm.com>

Author: miss-islington

Lib/test/test_signal.py

@@ -840,11 +840,11 @@ def test_itimer_real(self):
     def test_itimer_virtual(self):
         self.itimer = signal.ITIMER_VIRTUAL
         signal.signal(signal.SIGVTALRM, self.sig_vtalrm)
-        signal.setitimer(self.itimer, 0.3, 0.2)
+        signal.setitimer(self.itimer, 0.001, 0.001)
 
         for _ in support.busy_retry(support.LONG_TIMEOUT):
             # use up some virtual time by doing real work
-            _ = pow(12345, 67890, 10000019)
+            _ = sum(i * i for i in range(10**5))
             if signal.getitimer(self.itimer) == (0.0, 0.0):
                 # sig_vtalrm handler stopped this itimer
                 break
@@ -861,7 +861,7 @@ def test_itimer_prof(self):
 
         for _ in support.busy_retry(support.LONG_TIMEOUT):
             # do some work
-            _ = pow(12345, 67890, 10000019)
+            _ = sum(i * i for i in range(10**5))
             if signal.getitimer(self.itimer) == (0.0, 0.0):
                 # sig_prof handler stopped this itimer
                 break